Is it possible to dynamically configure Tomcat?

It can be done partially. By including the Tomcat library into a servlet you can access a lot of internal stuff from Tomcat. You can get access to the real underlying objects instead of using the javax.* facade objects. You would have to learn more about Tomcat to be able to do a lot with it. I suggest you generate the API from the Tomcat source (like I did) and experiment with it.

For example, this is the source I used to obtain all the current active web applications running in Tomcat 3.2.1.
I hope this is useful for you.